Silicon oxide film formation by moisture oxidation, for example, can need more than 1,000 sccm or cubic centimeters/minute of high-purity water in a standard state in semiconductor manufacturing. For that purpose, the inventors earlier developed and disclosed reactors for generating high purity moisture as shown in FIG. 5 and FIG. 6.
The reactor shell 1 shown in FIG. 5 is formed by mating a reactor structural component 2 on the inlet side having a material gas supply joint 9 and a reactor structural component 3 on the outlet side having a moisture gas take-out joint 12. In the reactor shell 1, a reflector 8 on the inlet side is so clamped by screw bolts 5 as to face a material gas supply passage 7 and a reflector 11 on the outlet side to face a moisture gas outlet passage 10.
The inside wall surface of the reactor structural component 3 on the outlet side is provided with a platinum coated catalyst layer 13. The inside wall surface of the reactor structural component 2 on the inlet side and the outside surfaces of the reflector 8 on the inlet side and the reflector 11 on the outlet side are provided with a barrier coat 13a formed of a nitride such as TiN which will be described later.
The platinum coated catalyst layer 13 is formed on the barrier coat 13a of a nitride like TiN provided on the inside wall of the reactor structural component 3 on the outlet side by fixing the platinum coat 13b by vapor deposition technique, ion plating technique or the like.
In the reactor shell 1 shown in FIG. 6, there is provided a relatively thick reflector 22, and the inside surface of the reactor structural component 3 on the outlet side is provided with a platinum coated catalyst layer 13 formed of barrier coat 13a and platinum coat 13b. 
The inside surface of the reactor structural component 2 on the inlet side and the outside surface of reflector 22 are provided with barrier coat 13a but without the platinum coat 13b described in FIG. 5. Thus, the surfaces of the reactor structural component 2 on the inlet side and reflector 22 are not catalytic, thereby preventing O2 and H2 from reacting on those surfaces and raising the temperature locally.
Referring again to FIG. 5, hydrogen and oxygen, i.e., the material gases, are fed into the reactor shell 1 through a material gas supply passage 7 and are diffused in the interior space 6 by the reflector 8 on the inlet side and the reflector 11 on the outlet side 11 and comes in contact with the platinum coated catalyst layer 13. Upon coming in contact with the platinum coated catalyst layer 13, oxygen and hydrogen are increased in reactivity by the catalytic action of platinum and are turned into the so-called radicalized state. As radicalized, the hydrogen and oxygen instantaneously react into moisture at a temperature lower than the ignition point of the mixed gas without high-temperature combustion. The high purity moisture is then supplied to the downstream side through the moisture gas outlet passage 10.
Similarly, in the reactor shell 1 shown in FIG. 6, the material gases comprising hydrogen and oxygen are fed into the reactor shell 1 through the material gas supply passage 7 and hit against the reflector 22, diffusing in the interior space 6. The diffused material gases of hydrogen and oxygen come in contact with the platinum coated catalyst layer 13 and are converted into a radicalized state. As described above, hydrogen and oxygen instantaneously react to produce high purity moisture without combustion at a high temperature.
The reactor shell 1 of the construction as shown in FIG. 5 and FIG. 6 has attracted much attention in the semiconductor manufacturing technological field because it permits a substantial size reduction of the apparatus used for generating and feeding high purity moisture and can produce more than 1000 cc/minute in a standard state with a higher reactivity and responsiveness.
Another feature of the reactor shell 1 of FIGS. 5 and 6 is that hydrogen and oxygen are handled at a temperature, e.g., 400° C., at which no spontaneous ignition takes place. Moisture is produced by catalytic reaction alone, and thus high-purity moisture can be secured and supplied safely.
Furthermore, the inventors have developed a number of techniques to raise the catalytic reaction efficiency in moisture generation according to the aforesaid catalytic reaction. To be specific, the inventors have improved the structure of the reactor to reduce the remaining hydrogen in the moisture gas by increasing the reaction between hydrogen and oxygen. Also, the inventors have developed a technique for increasing the reaction between hydrogen and oxygen by gradually increasing the flow rate of hydrogen; and another method of raising the reaction between hydrogen and oxygen by starting the supply of hydrogen after the supply of oxygen while cutting off the supply of hydrogen earlier than oxygen.
As a result of those techniques, the reactor shell 1 as shown in FIG. 5 and FIG. 6 can produce and supply high-purity moisture almost free of residual hydrogen.
However, the semiconductor manufacturing line has a large number of treatment processes in which moisture is fed under reduced pressure, for example, several Torr. In those processes, hydrogen and oxygen under reduced pressure are fed into the reactor shell 1 from the material gas supply passage 7. Consequently, there is a possibility in those reduced pressure processes that, with the ignition point dropping, hydrogen will spontaneously ignite in the reactor.
FIG. 7 is an ignitability limit curve for a 2:1 (by volume) mixture of H2—O2 in a spherical container with a radius of 7.4 cm. The source of the curve is the third edition of a chemical handbook, fundamentals, II-406 published by Maruzen publishing company. The numbers on the ordinate indicate the total pressure of the mixed gas while those on the abscissa indicate the ignition temperature.
Assuming from FIG. 7 that when the temperature inside the reactor is set at 400° C. the total pressure of the mixed gas of hydrogen and oxygen is reduced to several Torr. FIG. 7 shows that the ignition point for several Torr of pressure is about 400° C. Under this condition, the ignition point approaches the set temperature, and hydrogen can ignite spontaneously in the reactor. If the set temperature is still higher, ignition will occur without fail.
As indicated in FIG. 7, the ignition point of hydrogen sharply drops as the total pressure of the mixed gas of hydrogen and oxygen decreases. Even if the temperature is so set that hydrogen will not ignite when the total pressure is high, it can happen that hydrogen will suddenly ignite if the total pressure drops. If hydrogen ignites in the reactor, its flame flows back toward the upstream side through the material gas supply passage 7 and there is danger that combustion will take place in the area where hydrogen and oxygen are mixed, melting and breaking the piping and causing a fire to spread outside the reactor.
Another problem with the reactor of FIGS. 5 and 6 for generating moisture is that since the moisture-generating reaction is an exothermic reaction, the generated reaction heat will overheat the whole of the reactor shell 1 and the generated vapor steam. For example, when water vapor is produced at the rate of 1000 cc/minute, the temperature of water vapor reaches 400-450° C. because of self-heating. If the moisture generation is further increased, the temperature of water vapor will exceed 450° C. and approach the ignition point of hydrogen and oxygen or 560° C., bringing about a very dangerous state.
To avoid such a possibility, the upper limit of the moisture generation in the reactor for generating moisture of the prior art construction has to be 1000 cc/minute in terms of the standard state. One way to increase the moisture generation is to enlarge the reactor shell 1. But the size increase raises the costs and enlarges the size of the apparatus for generating and feeding moisture.
The present invention solves those problems with the prior art reactor and the earlier developed reactors, for generating moisture, including (1) the danger that ignition can occur when the total pressure of hydrogen and oxygen drops; and (2) moisture generation per unit volume is limited because the temperature of the reactor for generating moisture itself would rise and could cause ignition if the production of moisture is increased.